Biomedical subjects

J E Raymond

Publications and source records attributed to J E Raymond.

At least 19 recordsLinked to original sources

PubMed2000

Wholism for aging families: meeting needs of caregivers.

Family caregiving of a frail older person is an increasingly common phenomenon. Caregivers are confronted with new roles and responsibilities that provide both challenges and opportunities. Family issues that require expert nursing attention include role reversal, unresolved conflicts, caregiver immersion, elder mistreatment, and caregiving from a distance. Comprehensive geriatric assessment provides a foundation for intervening with families. Nurses are instrumental in providing a family perspective that meets the needs of frail older persons and their caregivers thus providing wholistic care.

Aged↗

PubMed1998

Successive episodes produce direction contrast effects in motion perception.

Motion coherence thresholds decline with an increase in the number of frames in a random dot kinematogram (RDK), indicating that motion information can be integrated across successive frames. We investigated whether such temporal integration would be disrupted by a brief interval (32-600 msec) inserted into a motion sequence, perceptually dividing it into two successive episodes. Both episodes consisted of only a few frames (between 3 and 15), with the first episode being 100% coherent and the coherence of the second episode being adjusted to determine threshold. In four experiments we observed that coherence threshold for motion in the second episode was elevated if the directions in the two episodes matched, was lowered if they were opposite, and was unaffected if they were orthogonal. This successive direction contrast effect did not vary with the duration of the interval, suggesting that it is not an adaptation effect. The result of varying the number of frames in the second episode suggests that these effects are not due to alterations in cooperative activity among motion detectors. We suggest that successive direction contrast effects may reflect activity of higher-order perceptual organization mechanisms.

Adult↗

PubMed1998

Priming reveals attentional modulation of human motion sensitivity.

Although recent fMRI and single unit recording studies have shown that attention modulates neural activity in motion sensitive areas of extrastriate cortex, these approaches cannot reveal qualitative or quantitative effects of attention on perception of motion. To investigate this, we asked observers to select one of two orthogonal directions in a brief, transparent dot display (prime) and then measured their sensitivity to global directional motion in a second uni-directional dot display (probe) presented a short time later. When probe direction matched the attended prime direction, sensitivity was degraded. But, when probe direction matched the ignored prime direction, sensitivity was enhanced, even though both components were of equal physical strength. Sensitivity was unchanged for directions opposite to either previously seen direction. Neither sensory adaptation nor opponent direction mechanisms can account for these data. Rather, processes initiated by visual selection must underlie these dramatic changes in motion sensitivity.

Adaptation, Psychological↗

PubMed1998

Anomalies of motion perception in infantile esotropia.

PURPOSE: To quantify motion sensitivity in patients with infantile esotropia who, as a subgroup, have been previously reported to have abnormal oculomotor control. In addition, to probe abnormal binocular development as a factor underlying abnormal motion perception in infantile esotropia (IE), motion sensitivity was compared among participants with and without stereopsis. METHODS: Monocular sensitivity to leftward and rightward motion was assessed across the horizontal meridian, using partially coherent random dot kinematograms. Participants included 11 observers with IE, 5 observers with acquired esotropia, and 11 observers with normal eye alignment. RESULTS: Participants with IE showed no deficits in motion sensitivity to any visual field locations when motion thresholds were collapsed across direction. However, they showed an abnormal variation in directional anisotropy. Although sensitivity to centripetal motion was superior in both hemifields of control participants and in the temporal hemifields of participants with IE, a centrifugal bias was revealed in the nasal hemifields of IE. Stereoblind observers with acquired esotropia showed a normal centripetal directional anisotropy, whereas binocular observers with acquired esotropia showed directional anisotropy similar to that in the IE group. CONCLUSIONS: Motion perception, like oculomotor function in IE, is characterized by a variation of directional anisotropy for stimuli presented to the nasal hemifields. This finding supports the hypothesis that abnormal oculomotor control and motion perception in IE reflect a common disruption of the visual system. A similar variation of directional sensitivity in patients with acquired esotropia with normal stereopsis suggests that the interruption of binocularity is not the underlying cause of abnormal motion perception in IE.

Adolescent↗

PubMed1997

Motion coherence perimetry in glaucoma and suspected glaucoma.

Motion direction sensitivity in glaucoma patients, glaucoma suspects and controls was assessed perimetrically at 22 visual field locations using small random dot kinematograms and a motion coherence task. For foveal stimulus presentations, mean motion coherence sensitivity was normal in both patient groups. However, nearly all glaucoma patients and about half of glaucoma suspects (all with normal visual fields as assessed with static perimetry) had some deficit of motion sensitivity. These were most pronounced and most prevalent in the superior field at 15 and 21 deg eccentricity. Glaucoma appears to produce a reduction in the normal integrative visual function necessary for the perception of global motion in textured displays and this disruption is non-uniformly distributed across the visual field.

Female↗

PubMed1996

What is noise for the motion system?

Motion coherence thresholds in random-dot patterns have been widely adopted as a measure of performance in visual motion processing. However, there has been diversity in the type of "noise" in which a coherent motion signal has to be detected. Here we compare coherence thresholds for three ways of creating motion noise: dots replotted in random positions in each new frame; dots with a set displacement but following a random walk from frame to frame; or dots moving in random directions which remain constant for a given dot over a sequence of displacements. In each case, the signal dots may either remain the same throughout the display sequence, or the signal dots may be re-selected afresh on each frame ("different"). With our display (3 deg square, 120 msec exposure, velocity = 5 or 10 deg sec-1), all these different noise conditions yielded similar thresholds around 5-8%. There were some small but systematic differences between conditions. Thresholds in random-direction displays were consistently higher than those in random-walk or random-position displays, especially at the lower velocity. However, this effect is much smaller than would be expected from the increased standard error of the noise mean in random direction, perhaps because the motion system integrates information most effectively over a local region of space and/or time. Subjects" performance could not be explained by a strategy of identifying individual signal dots with extended trajectories. The similarity between random-walk and random-position thresholds implies that subjects do not exploit the marked differences in speed distribution between signal and noise dots in the latter case. The practical message for the design and interpretation of experiments using coherence thresholds is that the results are not much affected by the choice of noise, at least within the range of stimuli tested here.

Adult↗

PubMed1996

Directional defects in pursuit and motion perception in humans with unilateral cerebral lesions.

We tested motion perception and smooth pursuit in 26 patients with unilateral cerebral hemispheric lesions. We used random dot cinematograms to test motion direction discrimination. We measured pursuit gain as they followed a predictable sinusoidal target moving horizontally at three different frequencies, and an unpredictable horizontal step-ramp target in the ipsilateral hemi-field. Six patients had defects in motion perception when the targets were moving towards the side of the lesions ('ipsi-directional' defects) and two had bi-directional defects. Motion perception defects occurred with lesions of the junction of Brodmann areas 19 and 37, a putative human homologue of the monkey V5 complex. Seven patients had ipsi-directional pursuit defects, five of whom had damage to the posterior limb of the internal capsule. Only two patients had ipsi-directional defects of both motion perception and sinusoidal smooth pursuit. Four patients had ipsi-directional defects of motion perception alone, and five patients had ipsi-directional pursuit defects alone. The two patients with bi-directional defects in motion perception had normal sinusoidal smooth pursuit. Patients with lesions at the 19/37 junction and defects of motion perception alone had normal pursuit of unpredictable step-ramp targets in the ipsilateral hemi-field. In contrast, patients with ipsi-directional sinusoidal pursuit defects had decreased ipsi-directional and increased contra-directional velocities with step-ramp targets. No patient group had a motion-specific directional defect in saccadic accuracy. We conclude that neither predictable nor unpredictable pursuit is necessarily impaired by lesions of the 19/37 junction that cause ipsi-directional defects of motion perception. These dissociations between smooth pursuit and motion perception provide evidence that the pursuit system operates as an interconnected network with parallel pathways, rather than as a simple sequential hierarchy of cortical areas.

Adult↗

PubMed1995

Retinotopic and directional defects in motion discrimination in humans with cerebral lesions.

We investigated the discrimination of motion direction in peripheral and central vision in 23 patients with unilateral cerebral hemispheric lesions on computed tomography or magnetic resonance imaging. We used random dot cinematograms that determined a percent coherence motion threshold for 16 points in the peripheral field and for four directions separately in central vision. We measured asymmetry of right- versus left-field peripheral discrimination (retinotopic defects) and asymmetry of central discrimination for rightward versus leftward motion (directional defects), compared with normal subjects. Five patients had directional asymmetries of foveal motion perception, all worse for motion toward the side of their lesions. One patient had a bidirectional defect for the perception of horizontal motion. For 3 of these 6, the average of all horizontal and vertical motion discrimination thresholds was also elevated. Two had contralateral retinotopic defects. One of these also had an ipsidirectional foveal defect, but the other did not. The remaining 5 patients with ipsidirectional foveal defects had hemianopias that precluded testing for coexistent retinotopic defects. The lesions of the 6 patients with ipsidirectional defects overlapped in white matter underlying the lateral temporo-occipital cortex, at the junction of Brodmann areas 19 and 37. In contrast, lesions of patients without directional defects spared this region.

Adult↗

PubMed1995

Similarity determines the attentional blink.

When participants are required to respond to a target letter imbedded in a stream of rapid serially presented letters, perception of a 2nd target letter is impaired if the interval between the 2 targets is less than about 450 ms. This attentionally based posttarget suppression in visual processing, referred to as the attentional blink (AB), is not found when there is a brief pause in the stream immediately after the 1st target. To investigate the importance of posttarget stimulation in AB production, the categorical, featural, and spatial similarity of the immediate posttarget item to other items in the stream was manipulated. Although featural and spatial dissimilarity produced significant attenuation of the AB effect, categorical dissimilarity did not. Significant AB effects were found in all conditions, suggesting that the presentation of any patterned stimulus in close temporal proximity to the target provokes the AB.

Adolescent↗

PubMed1994

Directional anisotropy of motion sensitivity across the visual field.

There is an implicit assumption in most models of movement direction perception that sensitivity to motion is directionally isotropic, i.e. equal for movement in all directions. However, most previous research on directional effects on human motion perception have measured responses (e.g. manual reaction times) to suprathreshold stimuli rather than motion sensitivity. I investigated this possibility by measuring monocular sensitivity to motion coherence in small field random-dot kinematograms with global leftwards or rightwards motion as a function of eccentricity along the horizontal meridian in each eye of six observers. Although foveal motion sensitivity was isotropic, small but significant differences (about 0.1 log units) in sensitivity in favour of centripetal motion were observed at eccentricities between 5.0 and 12.5 deg. Motion anisotropy was significantly larger in the temporal than the nasal visual hemifield. In a second experiment, motion coherence thresholds for upwards and downwards movement were measured foveally and at +/- 5 deg on the vertical meridian. At the fovea, no difference in sensitivity to upwards vs downwards motion was observed but these vertical axis thresholds were significantly higher than foveal thresholds for movement along the horizontal axis. Directional anisotropy in favour of centripetal motion was present in the inferior visual field but directional isotropy was found for the superior visual field. Perhaps this generally heightened sensitivity to centripetal directions may function normally to facilitate figure/ground segmentation in the presence of centrifugally-moving background contours that typically accompany forward locomotion.

Adolescent↗

PubMed1994

Attention to visual pattern information produces the attentional blink in rapid serial visual presentation.

To-investigate the temporal allocation of attention, a series of 7 experiments using rapid serial visual presentation (RSVP) was designed to examine the relationship of the attentional demands of various target tasks to the production of the subsequent visual attentional deficit, or "attentional blink" (AB), recently reported by J. E. Raymond, K. L. Shapiro, and K. M. Arnell (1992). The principal finding is that AB occurs only when a target is an object and does not occur when the target is defined by a temporal interval. Target detection difficulty as estimated by d' analysis reveals no relationship between the attentional demands of the target and the production of the AB. A late-selection account of this phenomenon is offered in place of the early-selection account advanced in Raymond et al.'s previous report.

Adult↗

PubMed1994

The effects of displacement size and frame duration on the motion-incoherence aftereffect.

After motion adaptation, the perception of global movement direction in partially coherent random-dot kinematograms (RDKs) is temporarily impaired if the predominant direction of dots in the test stimulus matches that of the adaptation stimulus. The dependence of this motion-incoherence aftereffect on stimulus characteristics (displacement size and frame duration) of the RDKs used to produce and measure it were examined. In addition, the speed selectivity of the aftereffect was investigated. The results indicate that the motion-incoherence aftereffect depends on frame duration, not displacement size, and that it is coarsely velocity selective.

Adult↗

PubMed1993

Complete interocular transfer of motion adaptation effects on motion coherence thresholds.

The binocularity of visual mechanisms in humans can be investigated by measuring the interocular transfer (IOT) of visual aftereffects. Cells in extrastriate visual areas of macaque, e.g. the middle temporal (MT) area, are uniformly binocular, whereas cells in striate area V1 vary in their degree of binocularity. Therefore, IOT of aftereffects mediated by extrastriate cortex should be nearly complete compared to the partial transfer (about 70%) found for aftereffects thought to be mediated by V1. If MT and other extrastriate areas play a significant role in motion perception, then IOT of motion adaptation aftereffects on the perception of moving stimuli should be nearly complete. After motion adaptation, the perception of global movement direction in partially coherent random dot kinematograms (RDKs) is temporarily impaired if the predominant direction of dots in the test stimulus matches that of the adaptation stimulus. I measured the IOT of this motion incoherence aftereffect in four observers. Post-adaptation motion coherence thresholds were elevated equally for interocular and intraocular adaptation, indicating complete transfer of the aftereffect. Measurement of the classical motion aftereffect using the same stimuli and conditions showed partial or absent transfer. These data support the idea that extrastriate areas play a key role in motion perception and suggest that the motion incoherence aftereffect and the classical motion aftereffect may involve different mechanisms.

Adaptation, Ocular↗

PubMed1992

Temporary suppression of visual processing in an RSVP task: an attentional blink? .

Through rapid serial visual presentation (RSVP), we asked Ss to identify a partially specified letter (target) and then to detect the presence or absence of a fully specified letter (probe). Whereas targets are accurately identified, probes are poorly detected when they are presented during a 270-ms interval beginning 180 ms after the target. Probes presented immediately after the target or later in the RSVP stream are accurately detected. This temporary reduction in probe detection was not found in conditions in which a brief blank interval followed the target or Ss were not required to identify the target. The data suggest that the presentation of stimuli after the target but before target-identification processes are complete produces interference at a letter-recognition stage. This interference may cause the temporary suppression of visual attention mechanisms observed in the present study.

Adult↗

PubMed1992

Visual accommodation and sustained visual resolution in multiple sclerosis.

Many multiple sclerosis (MS) patients frequently experience transient blurring. We investigated the possibility that this symptom is due to the inability of patients to sustain an accommodative response to stimuli viewed at distances nearer than or farther from the individual tonus position of accommodation. In a group of MS patients and age-matched healthy control subjects, we measured (1) accommodative range and tonus position; (2) reaction time (RT) to detect a change in a small optotype (viewed in a Badal lens system) as a function of viewing distance; and (3) contrast sensitivity at a fixed viewing distance. MS patients did not differ significantly from healthy controls on near point, far point, pupil size, accommodative range, or tonus position measures. However, as a group, MS patients showed significantly slower RTs than controls to detect optotype changes for stimuli viewed at distances nearer to or farther from the individual tonus position of accommodation. All subjects showed significantly slower RTs to detect changes in optotypes viewed at extreme near and far optical distances compared to RTs to detect changes in stimuli viewed at the tonus position. This difference was significantly larger for MS patients than for controls. These data also suggest that dynamic dioptric factors contribute to the magnitude of contrast sensitivity deficits in this patient population and indicate that the relationship between the individual tonus accommodation position and viewing distance is an important variable in CS testing.

Accommodation, Ocular↗

PubMed1990

The effect of local luminance contrast on induced motion.

Recently it has been suggested that the magnocellular, as opposed to the parvocellular, subsystem of the primary visual pathway of primates subserves motion perception. This suggestion is partly based on the observation that both the visual responses of magnocellular neural units and certain motion perception phenomena have high contrast sensitivity and are only dependent on luminance contrast for a narrow range of low contrasts. Parvocellular units have low contrast sensitivity and are dependent on contrast for a wide range of values. In the present experiment, the effect of local luminance contrast on induced motion was measured using a nulling procedure to quantify the magnitude, of illusory motion perceived in a centre grating which was viewed against a moving surround grafting. Centre grating contrast was either matched to the surround or maintained at a low (2.5%) or high (60%) value. Surround contrast ranged from 2.5% to 60%. It was found that (1) centre contrast had no observable effect on the magnitude of the illusion, (2) induced motion was marginal or absent with low contrast but detectable surrounds, and (3) induced motion increased as contrast in the surround increased for the range of contrasts tested. This contrast response function is more similar to that of parvocellular than magnocellular units and therefore suggests that the parvocellular stream may play a role in some aspects of motion processing.

Adult↗

PubMed1989

Training of efficient oculomotor strategies enhances skill acquisition.

The present study investigated the hypothesis that efficient oculomotor behaviours can be acquired through practice on a series of simple tasks and can be transferred subsequently to a complex visuomotor task, such as a video game. Each of two groups of subjects were exposed to a different set of simple tasks, or drills. One group, the efficient eye movement experimental group, received training designed to minimize eye movements and optimize scan path behaviours, whereas a second group of subjects, the inefficient eye movement experimental group, received training designed to increase the frequency of eye movements. Oculomotor training was interspersed with practice on the video game. Performance of these two experimental groups in the video game was compared to a control group playing the video game but receiving no specific training and matched for total time in the experiment. The group receiving efficient oculomotor training exhibited significantly superior performance in the video game and fewer foveations than either the inefficient or control groups, which did not differ from each other. Overall there was a significant inverse correlation between the number of foveations in the game and game score. The results of this study are discussed in terms of their implications for the importance of oculomotor training in the acquisition of any complex perceptual motor task.

Adolescent↗

PubMed1988

Abnormal visual adaptation to flicker in multiple sclerosis.

A visual psychophysical adaptation procedure was used on patients with Multiple Sclerosis (MS) in an attempt to induce a temporary and local exacerbation of subclinical visual impairment. Using a flicker detection task, sensitivity before and after adaptation to a flickering stimulus was measured in 9 MS patients and 9 control subjects. Although only 22% of patient eyes had abnormal flicker sensitivity prior to adaptation, visual deficit was observed in 83% of eyes studied after adaptation. Of the 7 MS eyes studied for which no other sign or symptom of visual involvement was present, 5 were found to have visual deficits after flicker adaptation. In addition, 10 of the 11 eyes affected by MS showed an abnormal response to flicker adaptation. Recovery from the effects of adaptation was complete in all patients within 2 minutes. The results suggest that partial demyelination of visual pathway neurons may exist in patients without signs or symptoms of visual involvement. The prolonged stimulation provided during adaptation may produce a temporary fatiguing or conduction blockade of such neurons which may lead to reductions in sensory sensitivity.

Adaptation, Physiological↗